The present invention relates generally to luminaires. More particularly, the present invention pertains to LED luminaires used as a source of normal and emergency lighting.
There are conventional luminaires, such as internally illuminated emergency, directional or pathway guide lights, that are provided with a box-shaped fixture main body whose front side is opened. A lamp such as a cold cathode lamp is arranged within the fixture main body. A ballast or other source of operating power is accommodated within the fixture main body to power the lamp, and a display panel is attached on a front side of the fixture main body so as to cover the open portion.
However, such conventional luminaires require a high-voltage, high-frequency voltage to be applied between the electrodes of the cold cathode lamp in order to power and operate the cold cathode lamp as the light source. Therefore, the wires connecting the ballast to the cold cathode lamp decrease the power supplied to the cold cathode lamp because of the influence of a stray capacitances. This may decreases the light output of the cold cathode lamp, so that some efforts are necessary to make the wiring as short as possible.
Because the cold cathode lamp requires a high voltage to operate, the ballast must be shut off entirely to avoid accidents such as electric shock when an abnormality occurs in the lamp. The cold cathode lamp thus cannot be lit even at the time of disaster such as a power outage. In the case where the luminaire is operated by means of, for example, a remote control device so as to check circuit operation of the luminaire, the remote control may malfunction because of noise generated from the cold cathode lamp.
Other luminaires are conventionally offered which use a plurality of lamps having LED chips as a light source. In this embodiment, the luminaire powers a plurality of LEDs using a DC power source, such as a battery, having a variable power output. A switching element and a plurality of lamps are connected in series with the DC power source to control the switching element so that the current applied to the lamp becomes constant, thereby enabling the lamp to be lit with stability.
Further, such conventional luminaires, when used as an emergency guide light, use a lamp having an LED chip as a light source, so that the lamp can be powered by a lower voltage compared to a luminaire using a cold cathode lamp as a light source. It is thus not necessary to shut off the power circuit entirely to avoid accidents such as electric shock during a power outage, thereby realizing continuous lighting. The lamp also can be driven by a low-voltage DC power source, so that the noise effects can be relatively reduced.
Some prior art LED luminaires are provided with a reflector section made of silver with a high reflection efficiency. The reflector section is arranged around a blue LED chip including a GaN compound semiconductor, positioned at the bottom of an LED package. A translucent resin (such as a silicone resin) containing a yellow phosphor is filled within the package. This provides energy savings.
In the prior art luminaire described above, sulfur that penetrates the translucent resin reacts with the silver in the reflector section to generate silver sulfide on the surface of the reflector section. This blackens the surface of the reflector section, thereby deteriorating luminance flux by approximately 20% to 30%, depending on an amount of silver used in the reflector section. Moreover, since the amount of free sulfur varies depending on the usage of the luminaire, it is difficult to predict when the surface of the reflector section of the lamp will be blackened.
When the luminaire is used as a guide light in Japan, the standards for guide luminaires and escape guide systems of the Japan Luminaires Association must be complied with. The guide lights are classified according to a size of a display surface. For example, in an escape exit guide light and a route guide light, a luminaire having a display surface of 130 mm or more and less than 200 mm in length falls into Class C. A luminaire having a display surface of 200 mm or more and less than 400 mm in length falls into Class B. Class B is subdivided into Class B Type BH that has relatively high average brightness of the display surface, and Class B Type BL that has relatively low average brightness. Furthermore, for example, in the Class B Type, the average brightness of the display surface is defined for the escape exit guide light and the route guide light in both normal operation and in an emergency, respectively, as shown in FIG. 6.
In the prior art luminaires that use an LED light source, approximately 30% of luminous flux deterioration occurs due to the degradation of the translucent resin at lamp end of life. It would appear that the sulfuration of the surface of the LED reflector section causes about 20% of the luminous flux degradation at the beginning of lamp use. More specifically, in this luminaire, it would appear that approximately 50% of the luminous flux degradation at the beginning of use occurs at the end of life of the LED.
In addition, in the case where the luminaire described above is used as an escape exit guide light of Class B Type BH, it would appear that the average brightness of the entire display surface at the end of life of the lamp is set to a lower limit in JIL5502 (500 cd/m2), considering the luminous flux deterioration of the lamp due to the sulfuration of the surface of the reflector section.
In this case, however, the average brightness at the beginning of use is 500/(1−0.5)=1000 cd/m2, if considering the luminous flux deterioration due to the degradation of the translucent resin filled within the package. Therefore, the average brightness at the beginning of use exceeds 800 cd//m2 that is the upper limit in JIL5502, so that the average brightness cannot satisfy JIL5502.
Referring to FIG. 7, a conventional prior art luminaire is provided with a box-shaped package 11a″ including a concave portion 11j″ in a circular shape (in plan view) formed on a surface side. A pair of metallic electrodes 11e″ are made of silver and are arranged at the bottom inside of the package 11a″. An LED chip 11b″ is arranged within the package 11a″, die-bonded on one of the metallic electrodes 11e″ by solder or the like, and electrically connected to the other metallic electrode 11e″ via a bonding wire 11i″. A translucent resin layer 11d″ made of a polythiol curing epoxy resin having translucency is filled within the package 11a″. A protection film 11f″ made of silicon nitride is formed on the surface of the translucent resin 11d″ side of the metallic electrodes 11e″ for suppressing the generation of silver sulfide. An exposed portion around the LED chip 11b″ at the bottom inside of the package 11a″ out of the metallic electrodes 11e″ constitutes a reflector section 11c″ for reflecting light emitted from the LED chip 11b″. 
However, again referring to FIG. 7, there is a reliability problem when prior art luminaires 11″ use a protection film 11f″ made of silicon nitride and the like on a surface 11c″ of the LED reflector section.